This study presents a real-time cyber−physical system co-simulation testbed for microgrids. The proposed testbed consists of two parts, a power simulator and a communication simulator, which has the capacity to emulate a physical micro-grid with large numbers of power electronic devices and its cyber system at real time. Furthermore, an interaction interface approach based on Ethernet is presented to synchronise data between two distinct simulation systems, as well as establishing the mapping relationship between corresponding nodes of power systems and communication systems. Through the detailed models of microgrids and accurate emulation of the cyber system, the developed testbed provides a simulation environment for the verification of the microgrids control algorithm and the influence of cyber events on microgrids performance. A case study is provided to explain the complete simulation process and demonstrate the ability of the testbed.